Now track "active time" in procstats.

Associations now keep track of the time they are
actively involved in impacting their target application.
This is based on the procstate propagating through the
association being the same as the procstate of its target
process...  so it may count as active when there is
another reason for that process to be in the same state.

To do this, we now maintain a set of "tracking
associations" -- these are in-use associations that
we know we need to be tracking to determine whether
they are active.  This list is built based on whether
we at all consider an association during an oom_adj
computation, and at the end of that walked to determine
which of those associations are currently active.

Also add tracking of associations through external
provider references, with a tag name now needing to be
passed through so we can mark up the reason for the
external reference.

Test: manual
Bug: 110957691
Change-Id: I426a499834e20a9d7f2b439faf9cb398d9792fa2